The present invention relates to a device for preventing wafer materials held in a wafer cassette from contacting with each other. More particularly, the invention relates to a device which is mountable on a wafer cassette holding a plurality of wafer materials, which is referred to simply as "cassette" hereinafter, with an object to prevent the wafer materials from contacting with adjacent wafer materials so that the wafer materials can be safely handled without troubles due to mechanical damage caused thereto by contacting with each other.
It is a remarkable trend in the technology of handling wafer materials or, in particular, semiconductor silicon wafers that the diameter of the silicon wafers is under continued increase from 6 inches to 8 inches and further to 12 inches so that warping of the silicon wafer is now a very important and difficult problem in the art of semiconductor industry. When a plurality of silicon wafers having such a large diameter are held in a cassette in an uprightly standing disposition in parallel to each other, contacting of adjacent wafers eventually takes place due to warping of the wafers resulting in mechanical damages such as chipping in the periphery of the wafers. This trouble can of course be obviated to some extent when a large space is provided between adjacent wafers, though with a disadvantage that the number of wafers which can be contained in a cassette is necessarily so decreased. Another problem to be considered is that, when a plurality of large silicon wafers are taken out of a cassette apart from the respective alignment grooves by an automatic wafer-handling machine, a large space to ensure lift-up movement of the machine arms must be left above the cassette so that the width of the alignment grooves is also increased as the diameter of the silicon wafer is increased, resulting in a shaky condition of the wafers held therein to increase the chance of contact between adjacent wafers. While a silicon wafer of a 12 inches diameter has a thickness of only 0.7 to 1.2 mm, for example, the cassette holding such large silicon wafers has alignment grooves each having a large width of 5.0 to 8.0 mm so that the silicon wafers held in such alignment grooves are unavoidably in a shaky condition and are subject to be mechanically damaged even by a very gentle contact with the adjacent wafers.
FIG. 7 of the accompanying drawings is a perspective view of a typical wafer carrier for storage and transportation of wafer materials laid flat on a side surface and disassembled into parts, of which the cassette A is provided on each of side surfaces thereof with wafer alignment grooves B1, B2 and, after a plurality of wafers (not shown in the figure) are inserted into the cassette A and held in the wafer alignment grooves B1, B2, wafer-pressing members C1, C2 are mounted onto the cassette A in the front and in the rear of the cassette A, respectively. The cassette A thus holding the wafers therein is then put into the carrier body D and a gasket member E is mounted on an engagement groove along the periphery of the carrier body D. A covering F is mounted thereon. The carrier body D and the covering F are tightly connected together by mounting clamping members H, H onto a pair of engagement ribs G, G provided on the carrier body D and the covering F.
When the wafers held in the wafer carrier as described above are taken out by hand, the clamping members H, H are first removed from the pair of the engagement ribs G, G and then the covering F is removed from the carrier body D. The cassette A taken out of the carrier body D is then set on a cassette-tilting apparatus and tilted thereon by an inclination angle of 15.degree. to 75.degree. followed by removal of a wafer-pressing member C1 before taking out the wafers one by one. This way of taking out wafers from the wafer carrier is naturally very troublesome with such a large number of manipulation steps.
Since the wafer alignment grooves B1, B2 provided on the cassette A each have a sufficiently large width as to leave play spaces on both sides of the wafer when a wafer material is put thereinto, the wafers inserted into the alignment grooves are necessarily in a remarkably shaky condition so that, as is illustrated in FIG. 6B, the wafers W are eventually brought into contact each with the other with a risk of mechanical damage when the wafers are held in an upright disposition. This problem of contacting of wafers W can be avoided when the wafers W are held not in an upright disposition but in a tilted disposition by a certain angle of inclination. This is the reason for the use of a wafer-tilting apparatus when wafers are to be taken out of a cassette.